The invention relates to an automobile painting installation and a method using such an installation.
Installations for dispensing and applying paint to motor vehicles generally comprise a plurality of painting stations, manual or automatic, each connected to a plurality of paint dispensing circuits. Each paint dispensing circuit corresponds to a particular color and supplies each application station from a paint tank. The paint is circulated in the circuit to prevent it from deteriorating.
At each application station, the paint color to be applied is selected by a color change device, called a color changer, comprising a plurality of valves of which the inlet is connected to a paint dispensing circuit by a line and of which the outlet is connected to a feed line connected to the paint application device of the station. Between two applications of paint of different colors, this feed line is rinsed using a bleed system. The opening of the color changer valves is automated in order to automate the application of the paint.
The frequent use of the paint colors demands large capacity paint tanks, which must consequently be kept at some distance from the application stations for reasons of size, so that long pipe lengths are necessary. Due to the size of these dispensing circuits, a large quantity of paint is required to fill them (about 1 to 3 tons).
Dispensing circuits of this size are inconceivable for rarely used paint colors, especially since a small quantity of paint, about five liters, is needed to paint a car. These colors are hence usually applied manually but with a finish inferior to that of the common colors applied automatically. In certain installations, smaller tanks are positioned closer to the application stations to also reduce the length of the dispensing circuit. However, a non-negligible volume of paint is still necessary to load the dispensing circuit (several hundred liters) and the paint must be circulated permanently. Moreover, if the consumption of paint is too low, the paint deteriorates so that the quality and color are no longer satisfactory, and the product must be destroyed and replaced.
Thus, up until the present, the automatic installations used to apply a rare color paint to a vehicle, to obtain a good quality finish, require quantities of paint which are disproportionate to the quantities actually applied, so that a large quantity of paint deteriorates.
Furthermore, space considerations around each color changer preclude the direct connection of a dispensing circuit to a changer valve, making it necessary to use a line connecting the circuit to the changer. A color change or a circuit cleaning accordingly requires cleaning this connecting line. Such a bleed can only be obtained today using the color changer, implying the shutdown of the painting station and a decrease in the paint application rate in the installation.
Documents U.S. Pat. No. 6,090,450 and U.S. Pat. No. 5,221,047 describe methods and devices for recovering or cleaning the feed line between the color change device and the paint application device. In document U.S. Pat. No. 5,221,047, the paint is pushed in the feed line using a scraper, up to the application device. All the paint is thus used and a return line repositions the scraper at the inlet of the feed line. This first scraper is followed by a given quantity of solvent, and then by air following a second scraper, in order to clean the feed line. In document U.S. Pat. No. 6,090,450, a scraper circulates back and forth in the feed line. At the end of the paint application, the scraper pushes the remaining paint outside the line and the application device, and is then returned to its starting point. However, these cleaning methods are only used on a short length of feed line, and not for a larger closed circuit.
There is therefore a need for an automobile painting installation which, in addition to the known paint application, permits the automated application of paints of a rare color with low circulation, the recovery of the unused paint, and the bleeding of the system. These recovery and bleed steps must preferably be carried out without reducing the automated rate of paint application to the vehicles, that is, during the application of a common paint color.